The present invention relates to a single crystal rod pull-up growing apparatus.
FIG. 3 shows the arrangement of a principal portion of a single crystal rod pull-up growing apparatus.
In a chamber 10, a graphite crucible 14 is placed on a table 12, and a quartz crucible 16 is engaged in the graphite crucible 14. The graphite crucible 14 is surrounded by a heater 18 which is surrounded by a heat shield 20. When polycrystal line pieces are placed in the quartz crucible 16, and when electric power is supplied to the heater 18, the polycrystal line pieces are heated to form a melt 22. The upper end of a supporting shaft 24 is secured to the table 12, the supporting shaft 24 being rotated by a motor M1 and vertically driven by a motor M2.
On the other hand, a seed holder 28 is attached to the lower end of a wire 26, a seed crystal 30 being held by the seed holder 28. The wire 26 is rotated around the axis thereof by a motor M3 and wound and unwound by a motor M4. After the seed crystal 30 is downwardly moved and dipped into the melt 22, the seed crystal 30 is pulled up to grow a single crystal rod 32.
In addition, Ar gas is introduced into the chamber 10 through a solenoid valve 34, and the chamber 10 is evacuated through a solenoid valve 36 and a vacuum pump 38.
Modes for controlling single crystal rod growth include an automatic control mode and a manual control mode, and the automatic control mode is generally selected if possible. In the automatic control mode, the temperature of the melt 22, the surface height of the melt 22, the rotational speed of the quartz crucible 16 and the pulling-up speed and rotational speed of the single crystal rod 32 are automatically controlled. In the manual control mode, these conditions are controlled by the skilled operator operating control knobs and switches on a console panel while viewing the crystal growth state.
When the single crystal rod 32 is automatically grown in the automatic control mode, if a commercial power source is cut off, since the heater 18 is turned off, the temperature of the melt 22 decreases, and the single crystal rod 32 cannot be continuously grown depending upon the degree of the power failure. Even if the time of power failure is relatively short, since the speed of response of the melt 22 to temperature control is relatively low, the electricity supplied to the heater 18 is significantly changed when automatic control mode is continued except the term of the power failure. This sometimes makes the temperature of the melt 22 unstable and the growth of the single crystal rod 32 impossible. In a factory provided with many single crystal rod growing apparatuses, although each of the growing apparatuses must be appropriately controlled in a manual control mode after the recovery from power failure, preferable control of the motors M1 to M4 depends upon the power failure time, thereby causing a state of panic. As a result, the rate of success of growth of the single crystal rod 32 is decreased, and the production cost is increased.